This invention relates to a galvanic-cell gas sensor comprising a cathode and an anode adapted to come into contact with a gas to be detected and sealed in an electrolyte.
A conventional galvanic-cell gas sensor comprises a holder serving as a container to hold an acid electrolyte and having a window and a diaphragm of a water-repellent film of a macromolecular fluorochemical sealed therein, with a cathode of gold (Au) disposed in a segment holding the electrolyte and an anode of lead (Pb) disposed apart from the cathode.
This type of sensor holding an electrolyte has been required to have a liquid-tightness that in turn calls for a complex sealing structure. The use of lead as the unnecessarily large anode has made it extremely difficult to reduce the size of the container.
The anode A has a rod portion B at one end thereof formed by casting or other method or a rod Bxe2x80x2 of a metal having a high corrosion resistance to the electrolyte and planted on the anode, as shown in FIG. 5. Therefore, the anode has been disproportionally sized considering the service life of the sensor, and has hampered the size reduction of the sensor.
This galvanic-cell gas sensor eliminates the need to form the anode lead segment on the anode from lead (Pb) sheet, while permitting a reduction in the sensor size by coating an appropriate amount of Pb proportional to the sensor life on the anode through accurate control of coating time.
This galvanic-cell gas sensor eliminates the need to form the lead segment on the anode from lead sheet while permitting to reduce the sensor size by coating an appropriate amount of lead proportional to the sensor life on the anode through accurate control of coating time.
Thus, the object of this invention is to provide a galvanic-cell gas sensor of smaller size by making the anode size proportional to the sensor life.